There are presently many cellular radio or mobile telephone systems conventionally employed to provide high quality mobile communications over wide coverage areas. One such system, for example, is the digital mobile telephone system GSM (Groupe Special Mobile). Presently, developments relating to the GSM standard are controlled by the European Telecommunications Standards Institute (ETSI) under the Special Mobile Group (SMG) technical committee. The document entitled “GSM Technical Specifications,” released by the SMG and available from the Publications Office of the ETSI, sets forth the technical requirements of the GSM standard and is incorporated herein by reference. GSM technology is used in a very broad variety of applications, including, for example, handheld and portable devices, PCMCIA (Personal Computer Memory Card International Association) cards, personal computers, PDAs (personal digital assistant), adapter cards, modems, etc.
The demand for higher data transmission rates in the GSM system has pushed standards groups to consider new techniques for increasing the information rate. For high-bandwidth wireless communications, the ETSI has recently adopted a new modulation protocol called EDGE (Enhanced Data Rates for GSM Evolution). To achieve enhanced data rates, the EDGE protocol utilizes an eight-level phase shift keying (8PSK) modulation and multi-slot transmission technique. Moreover, EDGE-enabled wireless products are required to support 850-MHz Advanced Mobile Phone System (AMPS), IS-136 (a North American Digital Cellular digital speech transmission standard) in the 850-MHz and 1900-MHz bands, along with GSM and EDGE in some combination of the 900-MHz, 1800-MHz and 1900-MHZ bands in order to meet telecommunication carriers' requirements for a mobile telephone that can roam globally. The baseband section of a wireless EDGE-enabled device should therefore support a variety of modulation methodologies, such as FM, differential quadrature phase shift keying (DQPSK) and GMSK modems, along with IS-136, GSM, half-rate voice encoders (vocoders), etc. As a further challenge to designers, it would be desirable to implement all of these features in a cost-effective manner and in an architecture which occupies the smallest physical footprint to meet ever shrinking packaging requirements. Conventional techniques do not adequately address these issues.
The EDGE modulation protocol achieves greater modulation efficiency than the GMSK modulation protocol used in the GSM standard, although such modulation efficiency is achieved at the expense of a reduced system noise margin. As stated above, the EDGE technology defines a new high data rate physical layer, namely, an 8PSK modulation architecture, instead of a GMSK modulation protocol. With an 8PSK modulation architecture, the gross data rate increases by a factor of three over that of GSM, since each EDGE pulse or symbol carries three bits of information versus a one-bit-per-symbol rate for GSM. The EDGE modulation protocol is described in further detail, for example, in an article by Hari Shankar entitled “Emerging Technology Series #1: EDGE in Wireless Data,” Communication Systems Design, Vol. 6, No. 1, January 2000, which is incorporated herein by reference. However, although an EDGE modulation protocol may be more efficient compared to a GMSK modulation protocol, GSM systems are still widely employed. Accordingly, it would be desirable to include both a GMSK modulator (e.g., for voice communications) and an EDGE modulator (e.g., for high data rate communications) in a wireless EDGE-enabled product. Unfortunately, using conventional approaches, the increased physical size and power requirements of the product become an issue as a result of the inclusion of the two independent modulators and their corresponding timing and control circuitry.